The present invention relates to a power system with several power converters operated in parallel supplying a load.
The output of parallel convertors are normally connected together through decoupling diodes to a system load, so that reverse current through a failed converter can be avoided. Parallel power supplies can be used to provide redundancy and where a single converter cannot supply the load power requirements. The output voltage feedback signal for the parallel converters is supplied from the load side of the decoupling diodes to provide precise voltage regulation.
One of the problems with using the load voltage as a feedback signal to all the parallel converters, is that due to minor converter circuit component variations in the individual converters, the output voltage of each of the converters will be different. The converter with the highest output voltage will forward bias the decoupling diode. The output of this converter, minus the decoupling diode forward drop, becomes the regulating voltage for the other converters in parallel. The regulating voltage appears to the other converters as an indication of over voltage, causing the output of the other converters to be reduced. With the feedback voltage remaining constant, the output voltage of the other converters will go down to zero. This could give a false indication while the unit or units are still functional. No amount of precision in the converter components will correct this problem, since a slight variation in any of the sense elements can cause one or more converters to shut off. In some systems the converters are kept from shutting off and are kept in an idle mode in which they do not provide power to the load.
In some power supplies with parallel converters, the output current of the each of the converters is sensed. A correction in the output voltage for each of the converters is made by complex circuitry until each of the power supplies delivers equal currents. All the parallel converters are interconnected and dependent on one another for proper operation. Replacement of a failed converter while the system is operating, referred to as hot plug in, is not possible. Because of the cross cabling between converters and complex circuitry, repair and maintenance of parallel power systems of this type is difficult.
It is an object of the present invention to provide a parallel power supply system which allows the removal and replacement of a defective converter without shutting the system down.
It is another object of the present invention to provide a parallel power system in which any power converter can fail without affecting the overall operation of the system.
It is yet another object of the present invention to provide a parallel power system in which each of the converters provides power to the load.
It is still another object of the present invention to provide a parallel power system that has reduced circuit complexity.